1. Field of the Invention
This invention relates to a bearing arrangement for a turbine rotor of a turbine adapted to be mounted in a drill string and to be driven by the flow of drilling fluid, comprising a turbine chamber surrounding the turbine rotor and having an inflow side and an outflow side, a stator with an axle on which the turbine rotor is rotatably mounted, a cavity formed between the turbine rotor and the stator and accommodating at least one radial plain bearing and being separated from the turbine chamber by two relatively spaced constrictions formed between the stator and the turbine rotor, and an axial plain bearing constructed as a bearing ring seal which provides a first constriction.
2. The Prior Art
A bearing arrangement of the aforementioned type is known from DE 197 06 371 A1. In the known bearing arrangement, the second constriction separating the cavity from the turbine chamber is disposed on the inflow side of the turbine chamber and is formed by an axial ring gap which extends in opposition to the inflow direction and through which drilling fluid can reach the cavity and the bearing gap of the radial plain bearing associated with the cavity, in order to provide for the necessary lubrication. The ring gap is connected to the bearing gap through two radial gap sections and an axial gap section connecting the radial gap sections. The axial gap sections are maintained in open position by two opposite permanent magnets which also ensure continuous contact between the bearing surfaces of the axial plain bearing. The known configuration is intended to prevent the entrainment of abrasive solid particles in the bearing gap of the plain bearing. However, practice has shown that this object is not achieved to a sufficient degree with the known configuration.